Method and arrangement for cooling an exhaust system

ABSTRACT

The present invention relates to an arrangement for cooling an exhaust system of a vehicle having an internal combustion engine. The arrangement includes a controller for detecting an elevated temperature condition of the exhaust system, such as a so called hot soak condition, as well as detecting a predetermined engine operating status, such as either of an engine shutdown, a stopped or an idling status. A secondary air injection system may then be actuated to inject ambient air into the exhaust system thereby cooling said exhaust system.

TECHNICAL FIELD

The present invention relates to an arrangement for cooling an exhaust system of a vehicle having an internal combustion engine, and more particularly to a secondary air injection system comprising such an arrangement.

BACKGROUND AND SUMMARY OF THE INVENTION

In the field of motor vehicles which are operated by means of internal combustion engines it is a general requirement that the concentration of certain regulated substances in the engine's exhaust gas should be as low as possible. These substances are mainly present in the form of unburnt residues of hydrocarbons (HC), oxides of nitrogen (NOx) and carbon monoxide (CO). In today's motor vehicles equipped with gasoline engines, a purification of the exhaust gas is normally carried out by means of a catalytic converter, or catalyst, arranged in the exhaust system. In the contemporary so-called three-way catalyst, the major part of the above-mentioned substances is eliminated by means of various well-known catalytic reactions.

In addition, evaporative emissions occur when, for example, on hot days gasoline heats up and evaporates from both the gasoline tank and wherever fuel may be present throughout the engine. They are also released from a hot engine and exhaust system when the car is running and/or idling. After the car is turned off, the engine still remains hot for a period of time, and gas vaporizes then, as well, even when the car is parked. This condition is called “hot soak”.

An engine experiences a hot soak condition when the engine load is reduced or the engine is shut down after a period of operation at high engine load. Residual heat of the exhaust system and the engine heats the atmosphere in the engine compartment and the heat of the engine and exhaust system is allowed to soak back into the fuel system. Engine and fuel system component temperatures are elevated during such a condition, or in the so-called hot soak condition. The fuel system in the engine compartment may be heated above a temperature which causes vapour lock or percolation of fuel in the fuel system located near the intake system of the engine. Furthermore, pressure may build in the fuel system. If any of the fuel injectors drip, excess gas is likely to build up in the engine, making it hard to start. Still further, components arranged at or close to the exhaust system of the engine may suffer negative effects due to overheating thereof during the conditions described above.

A prior art apparatus, described in U.S. Pat. No. 4,327,674, for cooling a vehicle engine compartment comprises a motor-driven fan to cool the engine, circuit means adapted to drive the fan in the stopped condition of the engine, and a temperature switch means operably connected with said circuit means and actuated to drive the fan by detecting a hot soak condition of the engine compartment, whereby said fan is driven for a predetermined period when the engine is stopped after a heavy load operation.

A technical problem encountered with utilization of the air stream from an engine cooling fan as described above is that, although the above-mentioned arrangement results in a cooling of the exhaust system, it is not satisfactory either because of the space requirements of the ducting required to convey the air stream from the fan back to the engine exhaust or, conversely, to convey the engine exhaust forward to the air stream from the fan. Furthermore, the cooling fan will, in the prior art apparatus above, have to be run for a rather long period of time in order to provide for sufficient cooling during a hot soak condition.

The present invention is directed to providing an improved arrangement for cooling an exhaust system of a vehicle having an internal combustion engine, which has limited space requirements and is potentially less costly and complex to manufacture and has improved efficiency and operating characteristics and eliminates or at least reduces the effects of the above discussed problems as well as contributes to reducing evaporative emissions.

In one exemplary embodiment of the present invention, and arrangement for cooling an exhaust system for an internal combustion engine, includes: a secondary air injection system coupled to the exhaust system, said secondary air injection system including: a pump for introducing ambient air into the exhaust system via a supply channel; and a valve for selectively allowing said ambient air to be injected into the exhaust system; and a controller coupled to said engine and said secondary air injection system, said controller actuating said secondary air injection system to introduce ambient air into said exhaust system when an exhaust gas temperature is above a predetermined value and a predetermined engine condition is detected by said controller.

Therefore, quick and efficient cooling of an exhaust system of a vehicle having an internal combustion engine can be achieved through this injection of air into the exhaust system of the vehicle in response to a detected elevated temperature condition during a detected predetermined engine status.

Optionally, said predetermined engine status to be detected by this arrangement is either of an engine shutdown, a stopped or an idling status of said engine.

More optionally, said elevated temperature condition to be detected by this arrangement is a so-called hot soak condition after heavy load operation of said engine.

Detection of this so-called hot soak condition after heavy load operation of said engine as a requisite for injecting the cooling airflow will contribute in counteracting the negative effects normally associated with the so-called hot soak condition as well as to component protection, especially of components arranged at or close to the exhaust system, and the reduction of evaporative emissions.

It will be appreciated that features of the invention are susceptible to being combined in any combination without departing from the scope of the invention as defined by the accompany claims.

BRIEF DESCRIPTION OF THE DRAWINGS

By way of example only, embodiments of the present invention will now be described with reference to the accompanying drawings wherein:

FIG. 1 is a schematic illustration of an example of and arrangement for cooling an exhaust system of a vehicle having an internal combustion engine according to the present invention; and

FIG. 2 is a schematic illustration of an exemplary method for cooling an exhaust system of a vehicle having an internal combustion engine in accordance with the present invention.

Still other features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein. The same reference numerals will be used for illustrating corresponding features in the different drawings.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to FIG. 1, there is illustrated schematically a simplified view of an internal combustion engine 1 having an arrangement 2 for cooling an associated exhaust system 3 in accordance with an embodiment of the present invention. A piston 4 is shown arranged within a cylinder 5 of the engine 1 in conventional manner. Fuel is injected into an air stream, illustrated by arrows 6, by means of a fuel injector 7 and its associated hosing 8. The fuel is injected into the air stream 6 inside an inlet manifold 9 of the engine 1 and mixes with the air stream 6, where after the air/fuel mixture in the inlet manifold 9 is introduced into the cylinder 5 by means of one or more inlet valves, not shown, in conventional manner. Following compression of the air/fuel mixture by the piston 4 the mixture is ignited to drive the piston 4 in conventional manner. Thereafter the produced exhaust gases, illustrated by arrows 10, are allowed to leave the cylinder by means of one or more exhaust valves, not shown, opening up a passage out into an outlet manifold 11 in conventional manner. The outlet manifold 11 is arranged to convey the exhaust gases 10 into one or more pipes 12 of the exhaust system 3 of the vehicle, of which exhaust system 3 FIG. 1 only illustrates schematically the initial piping 12 and a catalytic converter 13.

The arrangement 2 further comprises a sensor 14 for detecting an elevated temperature condition of the exhaust system 3. In an alternative embodiment one or more temperature sensors may be arranged at one or several locations along the extension of the exhaust system 3. The temperature sensor 14 is arranged to communicate with a controller 15, such as an engine control unit (ECU), e.g. via control wiring 14 a.

As described in the background and summary of the invention, an engine experiences a hot soak condition when the engine load is reduced or the engine is shutdown after a period of operation at high engine load. For further information on the so called hot soak condition reference is made to the background of the invention section.

Note that there are various methods for indicating when exhaust temperature reaches a pre-selected value. For example, an exhaust temperature sensor can be used which e.g. measures exhaust manifold temperature. Alternatively, the engine control unit can estimate exhaust temperature based on various operating conditions such as, for example: intake air temperature, engine speed, ignition timing, and engine air/fuel ratio. It will be obvious to the person skilled in the art that any one or a combination of the above discussed methods may be used for implementing a detection of the so called hot soak condition.

Controller 15 is further capable of detecting a predetermined engine operating status. The predetermined engine status to be detected is preferably either of an engine shutdown status, a stopped status (i.e. the engine status following engine shutdown) or an idling status of the engine 1, which statuses as further described in the background of the invention section are the engine statuses where hot soak is most likely to occur.

The arrangement 2 further comprises a pump 16 for selectively producing an airflow, illustrated by arrows 17, drawn e.g. from ambient air, illustrated by arrows 18, and a valve 19 for selectively allowing the produced airflow 17 to be injected into the exhaust system 3. The pump 16 preferably consists of an electrical air pump 16 and the valve 19 preferably consists of a check valve 19. The air pump 16 as well as the valve 19 are preferably arranged to be under the control of a control unit 15, e.g. via control wiring 16 a, 19 a.

The airflow 17, which usually has the temperature of the ambient air 18, may be arranged to be injected into the exhaust system 3 via a supply channel 20, which is attached to one or more of: a cylinder head of the engine 1; an engine exhaust manifold 11; exhaust pipes 12 of the exhaust system 3, or further via a supply channel arranged in a cylinder head of the engine 1.

The controller 15, is arranged to, in response to a detected elevated temperature condition during a detected predetermined engine status, enable the pump 16 to produce the airflow 17 and adjust the valve 19 to allow the airflow 17 to be injected into the exhaust system 3. Introduction of the airflow 17, having essentially the temperature of the ambient air, into the hot exhaust system 3 promotes cooling thereof and thus reduces the effect of so called soak back, which might otherwise cause undesired heating of the engine 1 or neighbouring components.

The arrangement for cooling an exhaust system 3 of a vehicle having an internal combustion engine 1 in accordance with the present invention is preferably realized using a conventional secondary air injection system. Such a system is, as is well known to the person skilled in the art, normally used in order to shorten the time required for the catalyst to reach the so-called “light-off temperature”, which is done through injecting secondary air into the exhaust gas. This secondary air is mixed with the exhaust gas immediately downstream of the engine's exhaust valves, resulting in an oxidation of the mixture consisting of the exhaust gases and the secondary air. The oxidation process is mainly due to the hydrogen which is present in the exhaust gases. The oxidation reaction generates a high amount of heat energy which is guided through the exhaust pipe 12 and fed to the catalyst 13, which subsequently becomes heated more rapidly.

This secondary air function is necessary during cold starts as the catalysts commonly used today provide a very high degree of exhaust purification at the appropriate operating temperature of the catalyst, i.e. a conversion of harmful exhaust gas components to carbon monoxide and water. However, from cold start a certain time period of heating is required in order for the catalyst to reach the operating temperature at which an optimum degree of purification may be obtained. The so-called “light-off temperature” of the catalyst is approximately 200-350° C. and may be defined as the temperature at which the catalyst provides a 50% degree of purification of a certain harmful component in the exhaust gases. During the initial warm-up phase of the catalyst, which e.g. may be approximately 30-90 seconds, the catalyst cannot operate in an optimum manner as regards the elimination of the harmful substances in the exhaust gases.

This preferred embodiment, comprising use of a conventional secondary air injection system, is based on the realization that the conventional secondary air injection system, originally envisaged for the purpose of heating the exhaust system 3, may be utilized for cooling of the same with only minor amendments to the control scheme of the components thereof.

Using such a conventional secondary air injection system the pump 16 may be a secondary air injection pump 16 of the secondary air injection system, which is arranged to pump ambient air 18 into the exhaust system 3. Furthermore, the valve 19 may be a valve 19 of the secondary air injection system. The controller 15 is preferably an integral part of the engine control unit (ECU) of the vehicle, adding to the engine control unit (ECU) the control scheme for realising cooling of the exhaust system 3 in accordance with the present invention.

Basing the cooling arrangement 2 on a conventional secondary air injection system, which is likely to anyway be present in the engine design, will reduce the cost and complexity of implementing an arrangement in accordance with the present invention.

A conventional secondary air injection system is normally arranged in connection with an internal combustion engine 1 for the above described purpose. Such an engine 1 is arranged to be supplied with an air/fuel mixture via an intake manifold 9. The engine exhaust 11 is connected to a catalytic converter 13, which preferably is a conventional three-way catalyst which is adapted to reduce the harmful substances carbon monoxide (CO), hydrocarbon (HC) and oxides of nitrogen (NOx) which are present in the exhaust gas 10. The exhaust gas 10 is discharged from the engine via an exhaust pipe 12. As the person skilled in the art should be thoroughly familiar with the above engine arrangement, further detail is not presented here.

Referring now to FIG. 2, there is illustrated schematically in a flowchart the steps of a method for cooling an exhaust system 3 of a vehicle having an internal combustion engine 1 in accordance with the present invention. Once the system is started, in one step 21 it is detected if an elevated temperature condition of the exhaust system 3 exists. The elevated temperature condition may be a so-called hot soak condition after heavy load operation of the engine. If detected, the flow follows the arrow path marked Y to an additional step 22, which may be performed simultaneously with the above step, and in which an engine operating status, such as either of an engine shutdown, a stopped or an idling status of the engine, is detected. In response to a detected elevated temperature condition during a detected predetermined engine status the flow follows the arrow path marked Y to a step of causing pump 16 to produce an airflow 17 and valve 19 to allow the airflow 17 to be injected into the exhaust system 3. Injection of air 17 may be maintained for a predetermined period of time or until a sufficiently low temperature of the exhaust system 3 has been achieved, as illustrated by the dashed loop-back arrow of the FIG. 2 flowchart. Should the engine 1 be operated outside of the pre-determined operating statuses, e.g. outside either of an engine shutdown, a stopped or an idling status, injection of air into the exhaust system 3 should normally be cancelled.

In a preferred embodiment of the method in accordance with the present invention the pump 16 being caused to produce the airflow 17 is a secondary air injection pump 16 of a secondary air injection system for an internal combustion engine 1 and the valve 19 arranged to allow the airflow 17 to be injected into the exhaust system 3 is a valve 19 of this secondary air injection system.

The above described arrangement 2 and method for cooling an exhaust system 3 of a vehicle having an internal combustion engine 1 using an arrangement 2 and method in accordance with the present invention, preferably comprising a secondary air injection system is useful on all internal combustion engines or so-called “Otto” engines and will prevent or reduce the effects of so called soak back using injection of secondary air into the exhaust system thereof. The arrangement 2 enables a reliable cooling system to be designed whilst keeping the cost as low as possible, especially when an already present secondary air injections system is used for the implementation of the inventive arrangement 2 and method.

In accordance with the present invention there is also envisaged a secondary air injection system for an internal combustion engine 2 having a secondary air injection pump 16, which is arranged to be controlled by an engine control unit 15, which secondary air injection system comprises an arrangement 2 in accordance with the present invention and as described above.

Furthermore, in accordance with the present invention there is envisaged an automotive vehicle having an internal combustion engine 1 having a secondary air injection system comprising an arrangement 2 in accordance with the present invention and as described above.

Modifications to embodiments of the invention described in the foregoing are possible without departing from the scope of the invention as defined by the accompanying claims.

Thus, while there have been shown and described and pointed out fundamental novel features of the invention as applied to a preferred embodiment thereof, it will be understood that various omissions and substitutions and changes in the form and details of the devices illustrated, and in their operation, may be made by those skilled in the art. It is the intention, therefore, to be limited only as indicated by the scope of the claims appended hereto. 

1. An arrangement for cooling an exhaust system for an internal combustion engine, comprising: a secondary air injection system coupled to the exhaust system, said secondary air injection system comprising; a pump for introducing ambient air into the exhaust system via a supply channel; and a valve for selectively allowing said ambient air to be injected into the exhaust system; and a controller coupled to said engine and said secondary air injection system, said controller actuating said secondary air injection system to introduce ambient air into said exhaust system when an exhaust gas temperature is above a predetermined value and a predetermined engine condition is detected by said controller.
 2. The arrangement according to claim 1, wherein said predetermined engine condition is an engine shutdown.
 3. The arrangement according to claim 1, wherein said predetermined engine condition is a stopped engine.
 4. The arrangement according to claim 1, wherein said predetermined engine condition is an idling engine.
 5. The arrangement according to claim 1, wherein said supply channel is attached to one or more of: a cylinder head of the engine; an engine exhaust manifold.
 6. The arrangement according to claim 1 wherein said controller controls said secondary air injection system to discontinue introduction of air into exhaust system once said exhaust gas temperature is at or below said predetermined value.
 7. A method for cooling an exhaust system for an internal combustion engine, comprising: detecting an elevated temperature condition of the engine exhaust system; detecting an engine operating condition; and in response to said detected elevated temperature condition during said detected predetermined engine status, injecting air into the engine exhaust system.
 8. The method according to claim 7, wherein said detecting of said engine operating condition of the exhaust system comprises detection of engine shut-down after heavy load operation of the engine.
 9. The method according to claim 7, wherein said detecting of said engine operating condition comprises detection of stopped or idling operation of the engine.
 10. The method according to claim 7 further comprising discontinuing air injection into the engine exhaust system once said elevated temperature condition is no longer detected. 